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The world lived for half a century with the constant specter of nuclear war and its potentially devastating consequences. The end of the Cold War took the potency out of this Armageddon scenario, yet the existential dangers have only multiplied. Today the technologies that pose some of the biggest problems are not so much military as commercial. They come from biology, energy production, and the information sciences -- and are the very technologies that have fueled our prodigious growth as a species. They are far more seductive than nuclear weapons, and more difficult to extricate ourselves from. The technologies we worry about today form the basis of our global civilization and are essential to our survival.